Apparatus for twisting helical fins and bonding them to tubes



Feb. 2, 1954 J. w. BROWN, JR 67,

APPARATUS FOR TWISTING HELICAL FINS AND BONDING THEM TO TUBES 3 Sheets-Sheet 1 Filed May 1, 1947 FIG. 3

INVENTOR. JOHN W BRowN, JR. BY

ATTORNEYS.

Feb. 2, 1954 J. w. BROWN, J-R 2,567,852

APPARATUS FOR TWISTING HELICAL FINS AND BONDING THEM TO TUBES Filed May 1, 1947 3 Sheets-Sheet 2 1N VEN TOR. I

A TTOPNEYS 8 JOHN W BRowN,dR.

Feb. 2, 1954 J. w. BRQWN, JR

APPARATUS FOR TWISTING HELICAL FINS AND BONDING THEM TO TUBES Filed May 1, 1947.

5 Sheets-Sheet 3 mZON 0253a mZON 02-02mm f Maw ozazom h OE I I I l I l l I Il|1lll||l IIIIIII T. N N mo/ WM J 6 Y B ATTORNEYS Patented Feb. 2, 1954 APPARATUS FOR TWISTING HELICAL FINS AND BONDING THEM TO TUBES John W. Brown, Jr., Lakewood, Ohio, assignor to Brown Fintube Company, Elyria, Ohio, a corporation of Ohio Application May 1, 1947, Serial No. 745,153

3 Claims.

This invention relates to apparatus for forming spirally finned tubes for heat exchangers and the like and more particularly to the formation of such tubing in which the fins are twisted while hot to the ultimate or hel cal shape.

Finned tubes in which the fins are formed about the tube in long helices as contrasted with tubes in Which the fins are parallel to the tube axis are desirable in some installations where the commodity contacting the fins is to be given a degree of turbulence in its motion along the tube. Finned tubes in which the fins lie parallel to the tube axis and apparatus by which such finned tubes are made are illustrated in my pending application Serial No. 727,598, filed February 10, 1947 and assigned to my present assignee, now Patent No. 2,572,593, granted October 23, 1951.

It is a general object of the present invention to provide an improved apparatus for making spiral fin tubes. Another object is to provide apparatus by which a plurality of fins are simultaneously twisted into spiral shape while they are hot and relatively soft. A further object is to provide for simultaneously bonding fins to a tube and twisting the fins to the desired spiral shape while they are still hot. Still another object is to provide a single heating source located inside of the tube so the tube and fins may be passed over it to raise successive annular increments of the fins and tube to a temperature suificient to form the bond and also permit ready deformation of the fins to the desired spiral shape.

Other objects of the invention will become apparent from the drawings and from the following description and the novel features are set forth in the claims.

In the drawings: Figure 1 is a perspective view illustrating a section of finned tube made according to my invention; Figure 2 is a longitudinal section through one form of apparatus used with the present invention; Figure 3 is a section through Figure 2 as indicated by the lines 3-3 thereon; Figure 4 is a longitudinal section on an enlarged scale of the head by which the fins are formed to a spiral shape; Figure 5 is a section through Figure 4 as indicated by the lines 5-5 thereon; Figure 6 is a section through the forming head as indicated by the lines 6& on Figure 4; and Figure 7 is a diagrammatic illustration of my method.

As shown in Figure l of the drawings, a finned tube made according to my invention may comprise a tubular conduit member T to which a number of spiral fin members H are secured.

2 Each fin member is preferably of channel cross section and comprises a base portion l2 and two fins it. An alternative form of fin that is not illustrated herein but that may be embodied in conduits made with the apparatus and method of the present invention is of L-shaped cross section with the base of the L secured to a tubular conduit T and the arm of the L acting as a heat exchanger fin corresponding to one of the fins 14. It will be evident to those skilled in the art that the transfer of heat between the tube T and the fins I i must take place through the base portion l2 and to this end. I secure the channel members to the tube by a fusing or bonding operation performed as hereafter described.

During the bonding operation the tube and a mandrel are moved axially relative to each other and the tube is slowly rotated relative to the mandrel. As the tube portion in which the bonding is complete is rotated with respect to the unbonded parts of the fins a twist or spiral is imparted to the fins where they have been heated to bonding temperature and in the case of each fin this becomes a permanent set upon cooling into the shape of a helix encircling the tube. Preferably the mandrel is held stationary during the forming operation and the tube is slid over a mandrel head at an unsupported end of the mandrel. The mandrel head is so constructed that a ring of hot burning gas is directed against an annular increment or segment on the inside of the tube adjacent to it. Provision is also made for projecting coolant, preferably in the form of cool air, from openings in the mandrel head against an adjacent annular portion on the inside of the tube that previously has been heated. As the tube and the mandrel head are moved lengthwise relative to each other successive annular increments of the tube and fins will first be heated to a temperature at which the desired bonds may be formed and at which the fins may be bent readily to spiral shape, and then cooled as they pass on over the head of the mandrel. It is important that the mandrel head and tube be moved relative to each otherin such a way that the hot gas is never directed against an increment of tube in which the bonding has already been completed or the bond would be destroyed.

A series of elongate fin members extending substantially parallel to the axis of the tube are held fixed against it by rollers during the above described heating and cooling operation. Solder or other bonding material placed at the region to be bonded is melted and flows to form the bond after which the tube is cooled and hardened.

The fin members, when heated by the hot gas to bonding temperature, are also made soft enough to be twisted at the same time to a helical shape which they retain when they are cooled. The desired twisting, as described below, is accomplished by a torque applied to rotate the end of the tube and fin assembly that has already been bonded, while the unbonded portions of the fins are held stationary. The portion of the tube to which fins have not been bonded is not restrained against rotating except by the friction of unbonded fins against it, hence it is relatively free to rotate, and the tube itself is not subjected to any severe trains and ordinarily is not twisted to any substantial extent. As stated, it is perferable to move the tube with respect to a fixed mandrel and for this purpose a plurality of rollers are provided that ride in the channels of the respective fins and are urged by springs toward the tube axis firmly to hold the fins in place against the tube during their movement in the bonding and forming process.

Referring now to Figure 2 it will be seen that the rollers are mounted on a frame that also supports one end of the mandrel. This frame comprises a pair of parallel I-beams I! mounted on a suitable bed, not shown. At one end the I-beams support a post '26 to which is secured a fixture 23 adapted to receive and clamp the fixed end of av hollow mandrel 25 that is spirally grooved on its exterior as hereafter described. Near the end of the frame opposite the mandrel supporting post 29 are two sets of clamping and guiding rollers supported on plates 21 and 23 that in turn are welded to and supported by cross plates 36 and 3|. These plates together with an additional cross plate 32 are secured to the beams i? to provide cross braces for the frame by which the other parts of the apparatus are supported.

The fins are twisted to their spiral shape by means of a head 33 with which they are engaged so that rotation of the head about the axis of the mandrel results in a similar rotation of the tube and fins. Although the force is applied at the end of the tube the twist takes place in the heated zone before the fins are immovably secured to the tube. The head is slidably mounted on the mandrel 25 and guided through a helical path by helical grooves 34 as it slides along the mandrel as hereafter described.

The sets of guiding and clamping rollers carried by each of the plates 27 and 28are identical except that, as shown in Figure 2, one set is reversed in position to face the other. Because of their similarity in construction only one set of rollers will be described, i. e., those attached to the plate 2'? and shown at the left in Figure 2.

Twelve channel shaped fins may be simultaneously secured to the exterior of a tube T by twelve rollers (Figure 3) in the embodiment of the invention illustrated herein. The provision of twelve channel members results in a total of twenty-four fins because there are two fins on each of the channels. Two of the twelve rollers are carried on axes that are fixedly mounted with respect to the plate 27 to provide means for accurately locating a tube with respect to the axis or" the mandrel. The other ten rollers are resiliently urged toward the axis, and in two instances also toward the opposite fixed rollers, to ccoperate in clamping the twelve channel members against the tube T. It will be apparent that a different number of rollers may be used depending upon the number of fins it is desired to bond to the tube.

The spring urged rollers are indicated at 35 and each such roller is mounted for rotation about a pin 3'! that is supported between the sides of a bifurcated arm 33 of a bell crank lever ll The lever ll is pivotally mounted on a pin 32 carried in a support as that is secured against the plate 21 by suitable bolts.

The other arm 59- of th bell crank 49 receives a pin 52 pivotally fastened to it. Suitable nuts 55 carried by the pin 52 bear against the plate 2'! and limit the inward or clockwise movement of the roller 35 (Figure 2). The roller normally is urged inwardly as far as the nuts permit by a coil spring 58 bearing at one end against the plate '21 and at the other end against the adjacent arm 50 of the lever til. Th clamping force exerted by the roller35 is dependent upon the spring 58 and the inward limit of roller travel may be adjusted by shifting the nuts 55.

The external periphery of each of the rollers 35 is shaped as best shown in dotted lines in Figure 3 to correspond to the internal form of those fins in which the rollers ride during the tube forming operation. Thus the outer edge is flat and about as wide as the fin base against which it bears while the outer side edges are slightly tapered to correspond to the angle at which the fins stand to the base.

All of the rollers shown in Figure 3 are mounted on arms 55 in this manner except the two rollers spaced apart and indicated at 35a. These two rollers lie on the under side of a tube received in th central aperture defined by the inner edges of the rollers and support the tube against dropping down out of alignment with other parts of the apparatus. At the same time the rollers 35a afford a positive limit against which the tube is held and prevent the tube from floating away from the mandrel axis by displacement as a group of all of the rollers that bear against it.

The rollers 35a each are supported on a pin 37 between bifurcations of an arm of a bell crank 40 as shown at the bottom of Figure 2. The bell crank 40 is pinned at 62 to a support 4 3 that in turn is secured to the plate 2'! in the same manner as are the arms carrying the rollers 35 at the top of Figure 2.

To provide a fixed support for the tube the rollers 35a beneath it are locked against bodily displacement. To thus lock rollers 35a pins 69 are pivotally secured at one end to the arms of the supporting bell crank it and at the other end are fixed in position with respect to the plate 21 by nuts 64 and 65 on opposite sides thereof.

The two sets of rollers carried by the plates 21 and 28 cooperate to clamp together a tube and a plurality of fins to be fed as a unit relative to a mandrel during the bonding or fusing operation. In the present embodiment of the invention the mandrel and the rollers 35 and 35a remain fixed with respect to each other and the frame while the tube and fins are moved relative to the bed and fed over the mandrel head on the mandrel 25. The tube is fed onto the mandrel at a fixed and continuous rate of speed during the heating and cooling operation with the result that it is fully seated on the mandrel after the fins have been bonded in place and formed to their spiral shape. It will be evident that various arrangements may be provided to produce relative movement between the tube and its fins on the one hand and the heating and cooling unit on the other hand and that such modifications may be made without departing from the scope of the present invention.

The mandrel used with the present invention has previously been designated 25 and stated to be mounted on a post 20 shown at the left hand side of Figure 2. It is hollow to carry a series of conduits for bringing fuel and coolant to a mandrel head 56 at the unsupported end as best shown in Figure 2. The mandrel head comprises a plurality of orifices 52 for directing hot burning gas against the inner surface of the tube T to heat it and the fins to the required temperature for bonding and also for softening the fins so they may be bent to the desired spiral shape. The gas is discharged from the orifices in a generally radial direction outwardly to impinge against the surfaces to be heated over an annular increment that is relatively short with respect to the longitudinal length of the tube. The gas not only heats the tube surface but at the same time the flame and its products of combustion travel along the tube toward the right (Figure 2) and exhaust at the end remote from the mandrel; in doing so the tube wall remote from the flame is preheated as it approaches the flame. The mandrel and mandrel head are more completely shown and described in my copending application referred to above.

The rate at which the tube is pushed onto the mandrel is dependent upon the amount of heat required to bend the fins and also to perform the bonding operation. When sufiicient heat is present in the tube and in the fins held against it by the rollers 35 and 35a the brazing or soldering material will flow. At the same time a helix or spiral will be imparted to the fins as the head 33 is guided as hereafter described through a helical path by the grooves 34.

As the tube with its fins, and the mandrel head continue to move with respect to each other the portion of the former that has been so heated will pass out of the ring of heating flame and into a position where coolant from orifices 5.4 will impinge upon it to cool the portion that has just been heated. During the time this cooling action is taking place on one increment of the tube the next and adjacent increment will be heated by the burning gas from the orifices, 52. While a stream of air ejected from the orifices 54 is the desired form of coolant used it will beapparent that other fluids may be employed depending upon the extent of the cooling effect that is sought. By the time the tube and fins have passed to the left (Figure 2) of the cooling region their temperature has been suificiently reduced to solidify the brazin or soldering material, thus bonding the parts together. Thus both the bonding and twisting of the fins are substantially completed within the region defined by the orifices 52 and bounded at the lefthand end (Figure 1) by the effect of the cooling air from the orifices 54. The operations of bonding and twisting are progressive and continuous as distinguished from an intermittent operation that consists of repeatedly starting and stopping the relative motion between the tube and mandrel.

The head 33 by which the helical shape is imparted to the fins is best shown in Figures 4, 5 and 6 as comprising two half sections and 16' provided with complementary ears 18 and 19 by which they are bolted together by bolts 80 in position about the hollow mandrel 25. Thehead is freely slidable along the mandrel and as it so moves is guided in a predetermined path two opposed helical grooves 34 in the. mandrel each of which is engaged by a, key 81 that. is.

fitted into a transverse recess in the end, of the head 33 and secured therein by bolts 82. The pitch or lead of the grooves is such that the head makes one complete revolution in approximately ten feet of mandrel length.

The head 33 makes engagement with the end of the tube to which the fins have been bonded so that as the head rotates when it moves along the mandrel the end of the tube turns with it.

To this end the head is provided with an axially extending opening 83 within which the tube and.

fins may be received until the end abuts an end wall 84 of the opening. To prevent relative rotation between the tube and head four longitudinal ribs 85, although more or less may be used, are provided on the inside of the opening 83. Each rib fits within one of the fin channels as shown. in Figure 6 and as the fins and tube are bonded together the entire tube assembly is turned with the head as the latter traverses its spiral path along the mandrel.

From the foregoing description it will be seen that as the right-hand end of the tube (Figure l) is pushed onto the mandrel the left-hand end of the tube, which is locked within the head 33, will push the head along in advance of it. The head in turn is guided in a helical path by the keys BI and thus rotates the tube and fins and imparts a. twist to the fins at the bonding region and, before they are firmly bonded in place on the tube. This bending of the fins is possible because of the temperature to which they have been heated by the fiame at the orifices 52 and by the further fact that they are not cooled until they reach the region of the rollers on plate where they are heated and before they are cooled by coolant from the orifices 54 sufiiciently for the bonding material to solidify. Because of the time required for the molten bonding metal to cool down sufficiently to solidify, the bond is completed in a zone to the left of the rollers 3'5. The finned tube ordinarily rotates inside the unbonded fin portions and rollers and is not permanently twisted although it may be somewhat twisted. depending on the resiliency of the metal from which it is made. The amount of twist imparted to the fins is small enough so the rollers on plate 21- need not be positioned transverse to axial planes through the. mandrel axis; however if desired they may be mounted with their axes slightly displaced from planes normal to the mandrel -:axis in conformity with the slight amount of divergence imparted to the spiral fins that shifts them out of parallel with the mandrel axis.

In practicing the invention embodied herein the required number of fins and the tube to which they are to be bonded are fed into the central aperture defined by the rollers positioned as shown in Figure 3. The respective rollers are adjusted so that each rides in a fin channel and thus the action of the springs 58 forces the rollers toward each other to clamp the fins and tube together. The rolling friction of the rollers is negligible and hence the fin-tube unit may be fed through the apparatus from right to left passing over the mandrel head as shown in Fig. ure 2. The mandrel is long enough to accommodate the desired lengths of tube and fins and permit the fin bases to be bonded to the tube over their entire length. After the bonding operation has. been-completed the assembled tube andfins: are'removedias a unit from: the mandrel a new assembly of tube and fins.

The sequence of steps just described as illus trated diagrammatically in Figure 7, in which, for the sake of convenience, only two fin members are shown. As the tube T moves to the left with respect to the rollers and the mandrel head, the hot gases from the head flow within the tube to the right preheating the tube, bonding metal and fins. Thus it may be considered that each increment of the tube passes through a preheating zone as indicated in Figure 7.

As each increment approaches the head 50, the heating becomes more intense and ultimately the tube, bonding metal and fins are heated to such an extent that the bonding metal is fused. This action may be considered as taking place in the heating and. fusing Zone indicated in Figure 7 although it must be understood that it is not possible to define this zone, or the other zones indicated in Figure 7, with precision. However, in any event, the tube and fin assembly is heated to a suflicient extent to fuse the bonding metal somewhere in the region of the fuel orifices 52 a of the head 50.

Promptly after the bonding metal is fused by the flame within the tube, the cooling action starts as each increment of the tube moves beyond the flame and reaches the cooling air jets 54. It must be remembered, however, that with the torch on the inside of the tube the inside of the tube reaches a temperature high enough to fuse the bonding material before the heat applied to the inside of the 'tube flows to the outside of the tube and fuses the outside of the tube. Also, the inside of the tube must be heated in excess of the temperature required for bonding in order for the outside to reach the bonding temperature. There is a time lag in the heating and similarly in the cooling, one reason for the la in the cooling being that the cooling air jets are directed against the interior of the tube. During the time that the heating and cooling are taking place each increment of the tube is being continuously progressed in the direction indicated by the arrow in Figure 7. Thus the effects of the heating and cooling on the exterior of the tube lag the application of heating and of COOIiIlg on the interior'of the tube. Furthermore, bonding materials such as ordinary solder and silver solder have substantial melting ranges, i. e., the bonding materials solidify the temperatures considerably below the temperatures at which they must be heated to reach the fluid state required for proper bonding. This increases the lag between the time of application of the cooling jets and the actual solidification of the bonding metal and the bonding of the fins to the tube. For these reasons, in practice it is ordinarily desirable to arrange the head 50 in advance of the rollers 35 as shown so that each increment of the tube travels through the cooling zone for a short distance before it reaches the rollers 35. The cooling takes place continuously after the tube has passed the jets 54 and therefore the cooling zone is indicated as being of indefinite length in Figure 7.

As explained above, the tube with fins bonded 8. yet become bonded to the exterior of the tube; the solder has not yet solidified, hence the tube can rotate within the fins and as a result the me are bent without imparting substantial torsional distortionto the tube itself. The fact that it is unnecessary to distort the tube not only prevents damage to the material of the tube but also substantially reduces the force required in pushing the tube through the apparatus.

Shortly after the fins have been bent into helical form the temperature of the assembly of tube and fins is reduced to such an extent that the bonding metal solidifies and the fins become firmly bonded to the exterior of the tube. This takes place in the region indicated by the bonding zone. Here again, as with the other zones, the precise location and length of the zone cannot be readily determined, but the bonding is completed after the fins have been bent into spiral form.

From the foregoing description it will be seen that I have provided an improved apparatus for forming spiral or helically finned tube in which the fins may be twisted simultaneously with the operation of bonding them to the tube.

I claim:

1. In apparatus for simultaneously bonding a plurality of elongate members to the exterior of a tube by heating aid members to bonding temperature and forming them to helical shape with respect to the tube axis, a frame, a mandrel fixed at one end to said frame, a head adjacent the other end of said mandrel, a plurality of nozzles in said head to burn fuel and direct the flame thereof toward a tube overlying said mandrel, a plurality of nozzles in said head to direct coolant against an annular increment of said tube, rollers carried by said frame and resiliently urged toward said tube to hold a. plurality of elongate members against the exterior of said tube in position to be bonded thereto while said tube and members, and said rollers and mandrel, are moved relative to each other to heat to bonding temperature and thereafter cool successive annular increments of said tube and elongate 7 members, a helical groove formed in said mandrel 7 adjacent said frame, a head on said mandrel to engage with said groove and be guided in a helical path thereby as it moves along said mandrel and members carried by said head to engage an end of said tube to prevent relative rotation between said tube and head to rotate said tube and twist said elongate members to helical shape at the increment thereof heated to bonding temperature.

2. In apparatus for making helical finned tubes, a mandrel adapted to extend within a tube, a burner carried by the mandrel and adapted to heat an annular increment of an assembly consisting of atube and a plurality of separately formed longitudinally extending as said burner and said assembly move relative to each other in the direction of the tube axis, a plurality of radially disposed rollers adapted to en-.

means and said rollers into a helical shape about the axis of said tube.

3. In apparatus for simultaneously bonding a plurality of elongate members to the exterior of 'a tube'by heating said members to bonding temperature and forming them to helical shape with respect to the tube axis, a frame, a mandrel fixed at one end to said frame, means carried by said mandrel to heat an annular increment of said tube as said tube is moved relative to said heating means, rollers carried by said frame and resiliently urged toward said tube to hold a plurality of elongate members against the exterior of said tube in position to be bonded thereto while said tube and members and said rollers and mandrel are moved relative to each other to heat to bonding temperature and thereafter cool successive annular increments of said tube and elongate members, a helical groove formed in said mandrel adjacent said frame, a head on said mandrel to engage with said groove and be guided in a helical path thereby as it moves along said mandrel, and members carried by said head to engage an end of said tube to prevent relative rotation between said tube and head to rotate said tube and twist said elongate members to helical shape at the increment thereof heated to bonding temperature.

JOHN W. BROWN, JR.

References Cited in the file of this patent UNITED STATES PATENTS Number Number Name Date Wilson Apr. 12, 1887 Sessions Mar. 6, 1928 Ruhr Mar. 24, 1931 Vance Oct. 27, 1931 Young Aug. 14, 1934 Nigro Apr. 9, 1935 Caberly May 12, 1936 Sims Aug. 3, 1937 Birmingham Feb. 8, 1938 Anderson Apr. 23, 1940 Tilley Aug. 5, 1941 Brown Nov. 4, 1941 Hansen Jan. 11, 1944 Hughey June 27, 1944 Thompson Dec. 11, 1945 Lyle Jan. 15, 1946 Brown Oct. 23, 1951 FOREIGN PATENTS Country Date Great Britain Feb. 19, 1925 

